<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        span {
            /* 
                将该元素变为块级元素
                display: block;
                将该元素变为行内元素
                display: inline;
                将该元素变为行内块元素
                display: inline-block;
            */
            display: inline-block;
            margin: 100px;
            /* border: 10px solid red; */
            border-top: 10px solid red;
            /* 透明 */
            border-left: 10px solid transparent;
            border-right: 10px solid transparent;
            border-bottom: 10px solid transparent;
        }

        p {
            margin: 0;
        }

        body {
            margin: 0;
        }

        h1, h2 {
            margin: 0;
        }
    </style>
</head>
<body>
    1231231212
    <span></span>
    <p>this is my test text</p>
    <h1>this is my test text</h1>
    <h2>this is my test text</h2>
</body>
</html>